1. Field of the Invention
The invention relates to a marker for marking the central portion of the cornea which is to remain uncut in radial keratotomy.
2. Description of the Prior Art
Incisional keratotomy, specifically radial keratotomy, and astigmatic keratotomy, are surgical procedures which alter the refractive characteristics of the cornea by making precise incisions in the cornea at specific locations to ultimately produce a specific desired change in the corneal curvature, thereby changing the corneal refractive power. An essential feature of radial and astigmatic keratotomy is the determination of the optical zone, which is the central portion of the cornea which is to remain uncut. Determining and marking the central corneal optical zone is accomplished using an optical zone marker of a desired diameter. The optical zone marker is comprised of a circular cylinder of a somewhat variable vertical height attached to a handle for manipulation purposes (FIG. 1). One end of the cylinder has a sharp pointed edge which is used to encircle and outline the central corneal optical zone when pressed on the corneal epithelial surface. The central optical zone is demarcated either by pressing the optical zone marker edge against the corneal epithelium producing a visible imprint when the marker is removed, or the marker edge is coated with marking ink which leaves an ink imprint on the cornea when pressed against the cornea.
One difficulty, however, in using existing corneal markers, is the problem of assuring that the cornea is visualized, and the central optical zone demarcated while viewing the cornea perpendicular to the long axis of the cylinder of the optical zone marker. Inadvertent off-axis viewing through the optical zone marker may result in accidental decentration of the optical zone demarcation on the cornea which will have the significantly adverse affect of causing the refractive surgery to be performed off center, and therefore, producing a sub-optimal result. Various attempts have been made to ensure that visualization through the optical zone marker is indeed parallel to the long axis of the optical zone marker. These techniques include requiring the surgeon to close one eye while viewing the optical zone marker through the operating microscope, and attempting to view the light reflex off the dome of the cornea in the center of the optical zone marker as best possible. Another means of attempting to ensure proper centration is the incorporation of a single center indicating pointer attached within the optical zone marking cylinder (FIG. 2). Although this additional design feature provides some improvement in centration capability, the operating surgeon is still not assured of visualization through the optical zone marker parallel to the long axis of the optical zone marking cylinder.
Another optical zone design incorporating "cross hairs" (FIG. 3) has also been developed in order to ensure central placement of the optical zone marker on the corneal surface. Again, the cross hairs do not provide for accurate alignment parallel to the long axis of the optical zone marker cylinder.